Light output from a GaAs semiconductor laser has a wavelength which covers from around 1 μm to the 600 nm range, while a GaN semiconductor laser has been developed to output light with a wavelength of 405 nm mainly for use of next generation DVD light source. Well known as a laser of wavelength between them, that is, between about 400 nm and the 600 nm range are an Ar laser (488 nm/515 nm) and a combination of YAG/YLF and SHG (532 nm), for example.
The combination of YAG/YLF and SHG (532 nm) is developed for high power use (W level) and the YAG/YLF and SHG market is rapidly expanded in the fields of a marker of Si board or the like and trimming or repairing of TFT liquid crystal. Particularly, since a “marker” is now in increasing demand because of expanding demand for CSP (Chip Size Package) to be implemented in a mobile device, application of particularly YAG combined SHG laser module thereto is becoming active.
Further, in the trimming and repairing area, demands for repairing a display defect of TFT liquid crystal display are rapidly increased against the backdrop of increased production of TFT liquid crystal displays.
On the other hand, as a low power use, it is applied to measuring instrument, printing devices, DNA analyzers and the like.
FIG. 4 shows a conventional structure of an SHG blue (oscillation wavelength of 473 nm) or green (oscillation wavelength of 532 nm) laser module (for example, refer to “The Review of Laser Engineering” December 1998, pp 861 to 866).
A blue wavelength conversion SHG laser module 25 utilizes as a laser crystal a YAG crystal 21 and as a pumping light source a wide-stripe semiconductor laser device 5 of emission width 50 μm and maximum output 500 mW.
Semiconductor laser light output from the above-mentioned semiconductor laser device 5 is gathered inside the YAG crystal 21 via a lens 20 to initiate laser oscillation with the fundamental of wavelength 946 nm from the YAG crystal 21. Then, an SHG device (PPMGLN: Periodically poled MgO—LiNdO3 crystal) 22 converts the wavelength to output wavelength converted blue light of wavelength 473 nm, which then passes through an etalon 23 and a mirror 24 to be output.
However, the above-described conventional technique has a problem such that the YAG crystal 21 is heated when the fundamental is emitted by laser oscillation and the wavelength of light emitted from the YAG crystal 21 is shifted from the set wavelength. When the wavelength is shifted, an output from the SHG laser module becomes unstable.
In addition, as the biotechniques including fluorescence microscope and fluorescence analyses have been developed, there are demands for an inexpensive visible light (400 nm to 532 nm) laser for fluorescence excitation. However, its suitable laser module has not been realized yet.